The synthesis of an aldehyde by hydroformylation is known in the art. A catalyst for such a process is generally a soluble complex of a Group VIII transition metal having a phosphorus containing organic ligand. It is also known that the selection of the catalyst for the hydroformylation reaction has an influence on the rate and selectivity to the product aldehyde(s). Bidentate ligands are particularly preferred for their combination of reactivity and selectivity.
A number of patents teach structures of bidentate ligands for hydroformylation reactions that may be used for the production of aldehydes. U.S. Pat. No. 5,235,113 teaches a hydroformylation process in which an organic bidentate phosphite ligand containing two phosphorus atoms linked with an organic dihydroxyl bridging group is used with rhodium as a homogeneous hydroformylation catalyst.
Hydroformylation processes involving organic bidentate ligands containing two trivalent phosphorus atoms, in which the two phosphorus atoms are linked with a 2,2'-dihydroxyl-1,1'-binaphthalene bridging group, have been described in U.S. Pat. Nos. 4,769,498, 4,668,651, 5,113,022, 5,059,710, 5,264,616, and 4,885,401. Additional examples appear in WO-A-9303839 and WO-A-9518089.
With respect to the hydroformylation process, U.S. Pat. No. 4,148,830 teaches the use of high boiling condensation products of the process as the solvent in recycling the catalyst system; and U.S. Pat. No. 4,247,486 teaches the use of a gas recycle to control the liquid level in the reaction and to control the build-up of high boiling components in the process stream.
These prior patents teach catalyst structures and improvements in continuous processes for hydroformylation, but none address the problem of isolating product, byproduct and catalyst, one from the other. Yet, in all hydroformylation processes, the catalyst must be separated from the reaction products. In the case of hydroformylations such as the present invention, where the desired reaction product is an aldehyde, it has proved difficult to separate reaction products, particularly the higher boiling products and byproducts, from the catalyst system.
U.S. Pat. No. 5,648,554 to Mori et al., teaches separation of the hydroformylation catalyst precursor and the high boiling byproducts by extraction of this mixture in a polar solvent. This patent does not demonstrate the proposed process with the actual catalyst system used in hydroformylation, and neither does this patent make any clear teaching as to ligand structures that are necessary for the process of the patent to be workable.
The present invention provides a process by which the reaction products, including the high boiling products and byproducts, may be easily separated from the reaction catalyst system. In the present process the catalyst system may be readily separated from reaction products and recycled for use in the process, thus providing longer active catalyst system productivity.